The prior art discloses a large number of combustible non-tobacco materials which have been proposed as substitutes for tobacco in the preparation of smoking products. Most of these materials do not have colors that are typical of tobacco. Consequently, it is usually desirable to add coloring agents to such materials to improve acceptance by smokers who are accustomed to tobacco-like colors associated with smoking products they consume.
Various coloring agents and techniques have been disclosed in the art for imparting tobacco-like colors to tobacco substitutes. For example, U.S. Pat. No. 3,638,660 discloses a tobacco substitute having appropriate dyes incorporated therein. U.S. Pat. No. 3,931,824 describes a cellulose-based tobacco substitute colored with agents such as carbon, iron oxide, food dyes, tobacco extracts, organic colorants and inorganic pigments. These agents are not entirely satisfactory because they may give rise to objectionable flavors upon smoking or they may be impractical due to economic considerations.
Another technique for coloring tobacco substitutes is described in British Pat. No. 1,553,326 wherein tobacco dust comprising particles of 75 microns or less in diameter is applied to the surface of previously shredded tobacco substitute material to impart a tobacco-like color thereto. While that technique is effective, it also tends to defeat the purpose of adopting tobacco substitutes, namely, the elimination of tobacco from smoking products.
Included in the various materials described in the art as suitable tobacco substitutes are a number of cereal grains. These cereal grains are disclosed in U.S. Pat. Nos. 3,964,494 through 3,964,498 and 3,977,412 through 3,977,415. They are usually treated to effect expansion of the kernels of grain and the expanded grain is then shredded and used directly as a suitable smoking material. The shredded, expanded grain typically consists of elongated strands which are compatible with cut tobacco used as filler in the manufacture of cigarettes. The shredded, expanded grain is preferably coated with tobacco dust as described in the above-mentioned British Pat. No. 1,553,326 in order to approximate the physical appearance of tobacco shreds.